Problem: Solve for $q$ : $23 + q = 18$
Solution: Subtract $23$ from both sides: $ \begin{eqnarray} \\ 23 + q &=& 18 \\ \\ {-23} && {-23} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{23 + q} &\hphantom{=}& \hphantom{18} \\ q &=& 18 {- 23} \\ \end{eqnarray} $ Simplify. $ q = -5$